Christopher Wirbelauer

Hydration behavior of porcine cornea crosslinked with riboflavin and ultraviolet A

PURPOSE: To examine the influence of a new crosslinking treatment on corneal swelling properties that correlate with the degree of crosslinking. SETTING: Department of Ophthalmology, Vivantes‐Klinikum Neukölln, Berlin, Germany. METHODS: Twenty freshly enucleated porcine eyes were crosslinked by applying the photosensitizer riboflavin and ultraviolet‐A (UVA) light (370 nm, 3 mW/cm2) for 30 minutes. After the eyes were treated and incubated for 24 hours in a moist chamber, 15 eyes were examined by biomicroscopy and optical coherence tomography (OCT); 5 eyes were examined by light microscopy. Five control eyes were included. RESULTS: Using light microscopy, a characteristic swelling pattern with 3 zones was identified in the crosslinked porcine cornea: an anterior intensely crosslinked zone of 242 μm, an intermediate partially crosslinked zone of 238 μm (hydration factor 2.2), and a noncrosslinked posterior zone of 1355 μm (hydration factor 2.7). A condensed OCT signal was demonstrated in the treated portion of the anterior stroma to a depth of 520 μm with a pronounced line at 540 μm, correlating with the combined anterior and intermediate layers after hydration in the histological analysis. In the nonhydrated state of the crosslinked cornea, the anterior zone was deduced to be 242 μm; the intermediate zone, 109 μm; and the posterior zone, 501 μm. Therefore, the maximum depth of the crosslinking effect was 351 μm. CONCLUSIONS: Collagen crosslinking using riboflavin and UVA led to a significant change in the swelling behavior of the anterior stroma, confirming prior findings that the crosslinking effect is strongest in the anterior half of the stroma. Crosslinked cornea did not induce a specific signal on OCT, and OCT is therefore not suited for clinical controls of the crosslinking effect.

Subthreshold (retinal pigment epithelium) photocoagulation in macular diseases: a pilot study

BACKGROUND Subthreshold (retinal pigment epithelium) photocoagulation is a new photocoagulation method, which treats the retinal pigment epithelium (RPE) and avoids damage to the neural retina. The initial results in this prospective pilot study on various macular diseases are presented. METHODS 12 patients with diabetic maculopathy (group I), 10 with soft drusen (group II), and four with central serous retinopathy (CSR) (group III) were treated and followed up for 1 year. Treatment was achieved using a train of repetitive short laser pulses (1.7 μs) of a green Nd:YLF laser (parameters: 527 nm, 100 and 500 pulses, repetition rate: 500 Hz, spot size: 160 μm, energies: 70–100 μJ). Laser energy was based on the visibility of test lesions on fluorescein angiography (50–130 μJ). Patients were examined at various times by ophthalmoscopy, fluorescein and ICG angiography, and infrared imaging. RESULTS After 6 months hard exudates disappeared in six out of nine patients in group I and leakage disappeared in six out of 12 diabetic patients. In group II drusen were less in seven out of 10 patients. In group III serous detachment disappeared in three out of four cases. Visual acuity was stable in all cases. None of the laser lesions was clinically visible immediately. After 1 day most lesions were visible as yellowish RPE depigmentation. After 3 months some of the lesions were visible as hyperpigmented areas but most were not. Fluorescein angiography showed leakage only in the first week. Infrared imaging showed that most lesions can be visualised in groups I and II after a period longer than 1 week as hyperreflective areas. CONCLUSION This study showed that subthreshold (RPE) photocoagulation is effective in some cases of diabetic maculopathy, drusens, and in CSR. Visibility of laser burns is not always necessary in the treatment of macular diseases presented here. Infrared imaging is an effective and non-invasive way of visualising subthreshold (RPE) laser burns.

Slit-lamp-adapted optical coherence tomography of the anterior segment

Abstract · Purpose: To evaluate the diagnostic potential of a slit-lamp-adapted optical coherence tomography (OCT) system as an in vivo imaging device for routine clinical examination of the anterior segment of the eye. · Patients and methods: In a pilot study, healthy volunteers and patients with different pathologies of the anterior segment were examined with a slit-lamp-adapted OCT system using 100–200 axial scans with 100-Hz line-scan frequency. The scan length is variable up to 7 mm, and the axial depth is 1.5 mm in tissue. · Results: The slit-lamp-adapted OCT system allowed direct biomicroscopic imaging of the measured area. Anatomic structures and morphological changes anterior to the attenuating iris pigment epithelium could be visualized with high accuracy. Biometric analyses of the cornea, the chamber angle, the iris and secondary cataract were possible. Complete demonstration of the chamber angle was difficult due to the backscattering properties of the anterior part of the sclera and the consequent shadowing of the most peripheral part of the iris. · Conclusions: Slit-lamp-adapted OCT is a useful diagnostic tool which allows in vivo microscopic cross-sectional imaging of the anterior segment and precise measurement of ocular structures.

Potential Use of Riboflavin/UVA Cross-Linking in Bullous Keratopathy

Background: Collagen cross-linking of the cornea has been shown by us to have an antiedematous effect in the cornea. The aim of the present study was to examine if this effect can be used for the treatment of bullous keratopathy. Methods: This clinical interventional case series included 3 patients (3 eyes) with bullous keratopathy due to pseudophakia, corneal transplant rejection, and Fuchs’ endothelial dystrophy. After dehydration for 1 day using 40% glucose, the central 8 mm of the cornea were abraded and cross-linked with the photosensitizer riboflavin and UVA (370 nm, 3 mW/cm2) for 30 min. Optical coherence tomography pachymetry measurements of the central cornea were performed at various time intervals. Results: Corneal thickness was reduced by 90.33 ± 17.04 μm on average 3 days after cross-linking and by 93.67 ± 14.22 μm after 8 months. The bullous changes of the epithelium were markedly improved, resulting in loss of pain and discomfort. Visual acuity was significantly improved in the case without prior stromal scarring. Conclusions: Cross-linking might become another useful tool in the treatment of bullous keratopathy. It is primarily suited for patients with pain symptoms, restricted visual prognosis or to extend the time interval for an upcoming corneal transplantation.

Corneal Optical Coherence Tomography Before and Immediately After Excimer Laser Photorefractive Keratectomy

PURPOSE To investigate the representation of the corneal structure with optical coherence tomography before and immediately after excimer laser photorefractive keratectomy. METHODS Twenty-four eyes of 24 patients with myopia and myopic astigmatism were prospectively studied. The corneal thickness and the corneal profile were assessed with slit-lamp-adapted optical coherence tomography preoperatively and immediately after excimer laser photorefractive keratectomy. RESULTS The attempted mean spherical equivalent of the refractive corrections was -6.7 +/- 3.6 (mean +/- SD) diopters with a mean calculated stromal ablation depth of 91 +/- 38 microm. The corneal optical coherence tomography was reproducible in all patients, demonstrating a mean decrease of central corneal thickness after epithelial debridement and excimer laser photorefractive keratectomy of 118 +/- 45 microm. The comparison of the calculated stromal ablation depth and the corneal thickness changes determined by corneal optical coherence tomography revealed a significant linear relationship with a correlation coefficient of 0.88 (P <.001). The flattening of the corneal curvature was confirmed in all patients with the optical coherence tomography system and correlated with the attempted refractive correction (r =.82, P <.001). CONCLUSIONS The slit-lamp-adapted optical coherence tomography system presented in this study allowed noncontact, cross-sectional, and high-resolution imaging of the corneal configuration. This initial clinical evaluation demonstrated that corneal optical coherence tomography could be a promising diagnostic modality to monitor corneal changes of thickness and curvature before and after excimer laser photorefractive keratectomy.

Monitoring corneal structures with slitlamp-adapted optical coherence tomography in laser in situ keratomileusis

Purpose: To monitor corneal structures with slitlamp‐adapted optical coherence tomography (OCT) in laser in situ keratomileusis (LASIK). Setting: Department of Ophthalmology, Vivantes Klinikum Neukölln, Berlin, Germany. Methods: In this prospective, nonrandomized, comparative clinical case series of consecutive patients who had LASIK for myopia and myopic astigmatism, the corneal structures were studied with slitlamp‐adapted OCT at a wavelength of 1310 nm. The central corneal thickness (CCT) and epithelial, flap, and residual stromal thicknesses were assessed preoperatively, immediately after surgery, on postoperative day 1, and then, on average, after 8, 35, and 160 days. Results: Twenty‐five eyes of 13 patients were included. The attempted mean spherical equivalent correction was −6.11 diopters (D) ± 2.16 (SD) with a mean calculated stromal ablation depth of 92 ± 24 μm. The CCT was 516 ± 26 μm preoperatively and 453 ± 40 μm postoperatively (P<.001). The epithelial thickness increased from 57.0 ± 7.7 μm preoperatively to 61.0 ± 7.5 μm postoperatively (P = .04). Imaging of the hyperreflective interface was possible in all patients for up to 15 months. The flap and residual stromal thickness was 211 ± 28 μm and 344 ± 48 μm, respectively, immediately after LASIK and 164 ± 21 μm (P<.001) and 284 ± 32 μm (P<.001), respectively, on postoperative day 1. There were no further significant changes during the follow‐up. The overall mean reproducibility was ±4.50 μm (coefficient of variation [CV] 0.94%) for CCT, ±4.99 μm (CV 8.57%) for epithelial thickness, ±6.25 μm (CV 3.55%) for flap thickness, and ±7.09 μm (CV 2.42%) for residual stromal thickness. Conclusion: Slitlamp‐adapted OCT can be used to longitudinally monitor the variable structures of the cornea, epithelium, flap, and residual stroma in LASIK.

Influence of indocyanine green staining on the biomechanical strength of porcine internal limiting membrane

Purpose: Indocyanine green (ICG) has recently been introduced to stain selectively the internal limiting membrane (ILM) of the retina for ILM peeling. The aim of the present in vitro study was to examine the effect of ICG staining on the biomechanical properties of porcine ILM. Methods: Two parallel 10 × 7 mm strips of central retina were prepared from each of the 40 porcine eyes. 0.005% ICG staining combined with white light illumination for 3 min was performed. Unstained, nonilluminated and 0.1% glutaraldehyde-treated specimens were used as controls. Biomechanical-force elongation measurements were performed using an automated material tester. The absorption spectrum of the ICG solution and the emission spectrum of the light source was measured. Results: After ICG staining of the retina combined with 3 min of illumination, a significant increase in ultimate force by 45% and a decrease in ultimate elongation by 24% was found. Without light exposure, there was no such effect, suggesting a light-dependent process. After 30 min of 0.1% glutaraldehyde treatment, there was an increase in ultimate force by 107% and a decrease in ultimate elongation by 66.6%. The absorption spectrum of the light source was continuous in the range from 400 to 800 nm including the absorption peak of ICG at 700 nm. Conclusions: ICG staining of the retina including the ILM causes a significant increase in the biomechanical stiffness thereby facilitating ILM peeling. The effect is due to a photosensitizing effect of ICG leading to collagen cross-linking.

Corneal shape changes after pars plana vitrectomy

Abstract · Background: The purpose of this prospective, controlled, clinical study was to investigate corneal shape changes due to pars plana vitrectomy (PPV) in patients with potential visual improvement postoperatively. · Methods: A total of 36 consecutive patients undergoing conventional PPV combined with or without macular surgery were studied. Sequential determinations of the corneal curvature by manual keratometry and corneal topography were performed preoperatively, during the first postoperative week, at 4 weeks and after 2–8 months (mean 4 months). · Results: The mean surgically induced keratometric astigmatism was 2.92±1.98 diopters (D) (P<0.0001) during the first postoperative week. After 4 weeks and 4 months the values decreased to 1.01±0.97 D and 0.67±0.43 D, respectively. Videokeratographic analysis confirmed significant curvature changes, with corneal steepening (P<0.008) which corresponded to the superonasal and temporal semimeridian, and flattening (P<0.008) along the inferior and inferonasal semimeridians. Corneal changes persisted in some cases for several weeks, partly in an asymmetric and irregular configuration. Shifts in axis to against-the-rule and oblique meridians were noted postoperatively with redistribution within preoperative values in 53% of the cases at 4 weeks after surgery. Subgroup analysis revealed that suture diameter, as well as the use of gas endotamponade, influenced the induced astigmatism. · Conclusion: A substantial increase of the corneal astigmatism and distinct shape changes can occur after PPV in the immediate postoperative period. Consecutive stabilization at preoperative values was observed after several weeks. The time course of the corneal curvature alterations should be considered in the postoperative management to detect refractive causes of inadequate visual acuity.

Continuous monitoring of corneal thickness changes during LASIK with online optical coherence pachymetry

Purpose: To assess the continuous intraoperative monitoring of central corneal thickness (CCT) changes during laser in situ keratomileusis (LASIK) using online optical coherence pachymetry (OCP). Setting: Department of Ophthalmology, Vivantes Klinikum Neukölln, Berlin, Germany Methods: In this prospective nonrandomized comparative clinical case series of consecutive patients, 32 eyes having LASIK for myopia, myopic astigmatism, or hyperopia were continuously monitored intraoperatively in real time with online OCP integrated into a clinical excimer laser. The intraoperative values were compared to the postoperative flap and residual stromal thicknesses measured with corneal optical coherence tomography (OCT) as well as the calculated myopic ablation depth. Results: Continuous monitoring with online OCP enabled intraoperative visualization of the CCT changes during LASIK. The CCT, flap thickness after the microkeratome pass, time‐resolved ablation, and residual stromal thickness were assessed. Intraoperatively, the mean flap thickness was 135 μm ± 38 (SD) and the mean residual stromal thickness, 286 ± 59 μm. The mean intraoperative flap and residual stromal thickness values were 43.7 μm and 15.4 μm lower, respectively, than the postoperative values assessed with corneal OCT (P<.001 and P = .005, respectively). The optically determined myopic ablation depth was 118 ± 37 μm, which was 28 μm higher than the nominal ablation depth. There was a significant correlation (P<.001) between the postoperative flap (r = 0.79) and residual (r = 0.88) thickness measured with corneal OCT as well as the calculated myopic ablation depth (r = 0.95). Conclusions: Intraoperative online OCP could be an important safety feature to monitor the flap and residual stromal thicknesses during LASIK. The individual ablation depth and possible dehydration effects were also monitored continuously.

First Experimental and Clinical Results With Transscleral Optical Coherence Tomography

BACKGROUND AND OBJECTIVE To evaluate the potentials of optical coherence tomagraphy (OCT) using long wavelength to penetrate highly scattering tissues of the eye and visualize the anterior chamber angle and the ciliary body. METHODS OCT images were generated by an experimental prototype in enucleated porcine eyes using as light source a superluminiscent diode with a wavelength of 1310 nm and a scan frequency of 60 Hz. The number of lateral scans was variable in a range from 100 to 400. RESULTS Infrared OCT was able to penetrate the sclera. The anterior chamber angle could be visualized completely and the ciliary body could be identified. However, it was not possible to penetrate the highly reflective iris pigment epithelium. CONCLUSION The use of infrared OCT allows penetration of the sclera, thus, providing complete visualization of the anterior chamber angle and limited demonstration of the ciliary body. Because of its higher resolution, it may represent an interesting noninvasive alternative to ultrasound biomicroscopy.